Polyolefin production

Details Polyolefin production Polyolefin production

2000-02-18

2003-02-04

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S127000, C526S134000, C526S351000, C526S943000, C556S053000, C502S117000, C502S152000

Reexamination Certificate

active

06515086

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a metallocene catalyst component for use in preparing polyolefins, especially polypropylenes. The invention further relates to a catalyst system which incorporates the metallocene catalyst component and a process for preparing such polyolefins.
BACKGROUND TO THE INVENTION
Olefins having 3 or more carbon atoms can be polymerised to produce a polymer with an isotactic stereochemical configuration. For example, in the polymerisation of propylene to form polypropylene, the isotactic structure is typically described as having methyl groups attached to the tertiary carbon atoms of successive monomeric units on the same side of a hypothetical plane through the main chain of the polymer. This can be described using the Fischer projection formula as follows:
Another way of describing the structure is through the use of NMR spectroscopy. Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm with each “m” representing a “meso” diad or successive methyl groups on the same side in the plane.
In contrast to the isotactic structure, syndiotactic polymers are those in which the methyl groups attached to the tertiary carbon atoms of successive monomeric units in the chain lie on alternate sides of the plane of the polymer. Using the Fischer projection formula, the structure of a syndiotactic polymer is described as follows:
In NMR nomenclature, a syndiotactic pentad is described as . . . rrrr . . . in which “r” represents a “racemic” diad with successive methyl groups on alternate sides of the plane.
In contrast to isotactic and syndiotactic polymers, an atactic polymer exhibits no regular order of repeating unit. Unlike syndiotactic or isotactic polymers, an atactic polymer is not crystalline and forms essentially a waxy product.
While it is possible for a catalyst to produce all three types of polymer, it is desirable for a catalyst to produce predominantly an isotactic or syndiotactic polymer with very little atactic polymer. C2-symmetric metallocene catalysts are known in the production of the polyolefins. For example, C2 symmetric bis indenyl type zirconocenes which can produce high molecular weight high melting isotactic polypropylene. The preparation of this metallocene catalyst is costly and time-consuming, however. Most importantly, the final catalyst consists of a mixture of racemic and meso isomers in an often unfavourable ratio. The meso stereoisomer has to be separated to avoid the formation of atactic polypropylene during the polymerisation reaction.
EP-A-0426644 relates to syndiotactic copolymers of olefins such as propylene obtainable using as a catalyst component isopropyl (fluorenyl)(cyclopentadienyl) zirconium dichloride. Syndiotacticity, as measured by the amount of syndiotactic pentads, rrrr was found to be 73-80%.
EP 747406 relates to the polymerisation of an olefin monomer to form a syndiotactic/isotactic block polyolefin, particularly a block polypropylene. A component of the polymerisation catalyst was a 3-trimethylsilyl cyclopentadienyl-9-fluorenyl zirconium or hafnium dichloride having an isopropylidene or diphenylmethylidene bridge.
EP-A-0537130 discloses the use of a C1 symmetric metallocene catalysts for the production of isotactic polypropylene. A preferred catalyst is isopropylidine (3-tert butyl-cyclopentadienyl-fluorenyl) ZrCl2. This catalyst has a bulky t-butyl group positioned on the cyclopentadienyl ring distal to the isopropylidine bridge. This catalyst has the advantage that it consists of only one stereoisomer and so no isomeric metallocene separation is required at the final stage of its synthesis. Whilst polypropylene preparation using this catalyst produces isotactic polypropylene, the polymer product has poor mechanical properties because of the presence of regiodefects and relatively low molecular weight.
Regiodefects occur in the polymer chain when, instead of producing a perfect isotactic polyolefin in which each monomeric unit is positioned head-to-tail in relation to the next, mis-insertions of the monomers occur so as to give either a head-to-head or tail-to-tail mis-match. These so called (2-1) regiodefects are partially transferred to the so called (1-3) insertion through an isomerisation process leaving units of four CH2 groups in the backbone of the polypropylene chain. This has a deleterious effect on the physical and mechanical properties of the polymer and results in low molecular weight isotactic polypropylene with a low melting point. EP-A-0881236 addresses this problem by providing isopropylidene (5-methyl-3t-butyl cyclopentadienyl fluorene) zirconium dichloride as part of a polymerisation catalyst. However, polypropylenes obtained using this catalyst have molecular weights (Mw) in the range 213900 to 458500 and a microtacticity characterised by the mmmm pentad in the range 82.8% to 86.8%. The melting temperature of these polymers is in the range 139.3 to 143.8.
EP-A-577581 discloses the production of syndiotactic polypropylenes using metallocene catalysts which have fluorenyl groups substituted in positions 2 and 7 and an unsubstituted cyclopentadienyl ring. The production of isotactic or syndiotactic/isotactic block polyolefins using these metallocene catalysts is not disclosed.
EP-A-0748824 describes the use of a chiral transition metal compound and an aluminoxane to produce stereoregular isotactic polypropylenes with a reported isotactic pentad content of up to 0.972. No data are presented in relation to the amount of monomer misinsertions in the polypropylene.
SUMMARY OF THE INVENTION
The present invention aims to overcome the disadvantages of the prior art.
In a first aspect, the present invention provides use of a metallocene catalyst component for the preparation of a polyolefin which comprises an isotactic or polyolefin syndiotactic/isotactic block polyolefin having a monomer length of up to C10, which component has the general formula:
R″(C
p
R
1
R
2
R
3
)(C
p
′R
1
′R
2
′)MQ
2
  (I)
wherein C
p
is a cyclopentadienyl ring substituted with at least one substituent; C
p
′ is a substituted fluorenyl ring; R″ is a structural bridge imparting stereorigidity to the component; R
1
is optionally a substituent on the cyclopentadienyl ring which is distal to the bridge, which distal substituent comprises a bulky group of the formula XR*
3
in which X is chosen from Group IVA, and each R* is the same or different and chosen from hydrogen or hydrocarbyl of from 1 to 20 carbon atoms, R
2
is optionally a substituent on the cyclopentadienyl ring which is proximal to the bridge and positioned non-vicinal to the distal substituent and is of the formula YR#
3
in which Y is chosen from group IVA, and each R# is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, R
3
is optionally a substituent on the cyclopentadienyl ring which is proximal to the bridge and is a hydrogen atom or is of the formula ZR$
3
, in which Z is chosen from group IVA, and each R$ is the same or different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, R
1
′ and R
2
′ are each independently substituent groups on the fluorenyl ring, one of which is a group of the formula AR′″
3
, in which A is chosen from Group IVA, and each R′″ is independently hydrogen or a hydrocarbyl having 1 to 20 carbon atoms and the other is hydrogen or a second group of the formula AR′″
3
; M is a Group IVB transition metal or vanadium; and each Q is hydrocarbyl having 1 to 20 carbon atoms or is a halogen.
Polyolefins produced using the metallocene catalyst component of the present invention are surprisingly found to have very good microtacticity, especially as determined by pentad distribution levels in 13C nmr. The polyolefins are also found to be substantially free of regiodefects. Accordingly, the polyolefins produced thereby have improved mechanical properties including a high weight average molecular weight typically in excess of 500,000 and melting point elevated by

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